Multiple-switchboard busy-test circuit an d apparatus



(No Model.) I 2 Sheets-Sheet l.

J. L. MOQUARRIEJ MULTIPLE SWITGHBOARD BUSY TEST CIRCUIT ANDAPPARATUS.

No. 487,853. Patented Dec. 13, 1892.

24255 25. Ira 671607:

1n: nouns vmns ca. wo'ro-umc" wnmma'rou. 04 c.

(No Model.) 2 SheetsSheet 2 J. L. MGQUARRIB. MULTIPLE SWITGHBOARD BUSYTEST CIRCUIT AND APPARATUS.

No. 487,853. Patented Dec. 13, 1892. I

N b A Inventor HE Norms PETERS 00., mom u'mou WASNINCITDN. ac.

whether a given line called for is at liberty or is already in use atanother section of the switch- UNITED STATES PATENT OFFICE.

JAMES L. MOQUARRIE, OF BOSTON, MASSACHUSETTS, ASSIGNOR, BY lVIESNEASSIGNMENTS, TO THE WVESTERN ELECTRIC COMPANY, OF ILLINOIS.

MULTlPLE-SWITCHBOARD BUSY-TEST CIRCUIT AND APPARATUS.

SPECIFICATION forming part of Letters Patent No. 487,853, dated December13, 1892.

Application filed April '7, 1892 Serial No. 428,205. (No model.)

To all whom it may concern.-

Be it known that I, JAMES L. MCQUARRIE,

and State of Massachusetts, have invented certain Improvements inMultiple-Switchboard Busy-Test Circuits and Apparatus, of which thefollowing is a speicfication.

This invention relates to multiple switchboards and to busy-testapparatus and circuits for use in connection therewith. Multipleswitchboards are now extensively employed in central telephoneexchanges, and of course require at each section some form of busy-testappliance whereby an operator at such section may at any time be enabledto ascertain board. It is now customary, in order that inductivedisturbance may be avoided, to construct metallic telephone-circuits.The ordinary busy-test which has in practice been found most convenientis to touch the frame of the desired plug-socket for an instantwith thetip of the plug-connector which is to be inserted and at the sameinstant to listen in the A click heard in the telephone or the absenceof sound in the telephone (as may previously be arranged) upon makingthe above test denotes that the line is at liberty and that theconnection may he proceeded With-that is to say, in some or.-ganiz'ations it is understood that if on making the test a clickingsound be heard in the telephone the tested line is already busy and thatif there be silence the line is at liberty,

7 while in other exchanges it is understood that if no such click beheard the line is busy,

, while the occurrence of the click indicates that the line is atliberty. It is not difficult to arrange apparatus for either mode oftesting. In metallic circuits the several socketframes have beenpermanently in connection with one side of the metallic telephonecircuit; and it has in practice been found with many such metalliccircuits on applying the plug for tests that a false signal has been re-A ceived, a click being observed in the telephone when the conditionsshould have called for its absence. Investigation of the subject hasshown that such false signals are attributable to the presence of acharge upon the affected upon the application of the test-plug dis- 5;

charges through the testing operators telephone in the form of acurrent, thereby producing in the said telephone a sound which is noteasily distinguishable from the true busy-test click.

The object of my invention is to provide a system of test appliances formetallic circuits which shall entirely avoid this liability to givefalse test signa s and to effect this desirable result without anyunnecessary complication in circuits or apparatus.

My invention is based on the principle that if the test-wire uniting theseveral plug-socket frames or test-contacts is normally severed from theline-circuit or made local in the central station in other wayssuch asby attaching a dead-earth connection to ita false test will beprevented. Accordingly I provide for eachaifected line a relay, whichnormally maintains the said desired localization of the test-wire andcontacts of such line and which may be connected with two contacts forits armature and arranged to ground the testwire through its ownelectro-magnet-ic helices and also to maintain a dead-earth connectionupon the return-line from the sub-station or which alternatively mayhave its armature provided with a single electrical contact and arrangedto ground the main conductor from the sub-station through theelectro-magnet and to apply a dead-earth to the return and test wiresand contacts. The former arrangement gives the positive signal in theoperators telephone when the line is busy and the latter gives thepositive signal when the line is not busy. The former plan is perhaps tobe preferred in that the positive signal toindicate a busy line is themore familiar and most frequently used mode of operation, while thelatter has an advantage in that the continuity of the circuit does notdepend upon the perfection of one of the relay-contacts. In both thetest-wire is normally cut off by the interposition of a dead-earth fromthe outside line, and in both the insertion of a plugconnector in anysocket of the circuit acts by energizing the electro-magnet of the relayto disconnect the said dead-earth connection and to establish thecontinuity of the return-line conductor through the plug-socket framesand also makes such a change in the electrical condition of the saidframes that when the test-plug is applied to any one of them a testindicating the present status of the line is indicated with certainty.

In the drawings which accompany and form a part of this specification,Figure l is a diagram illustrative of that exemplification of myinvention in which the helices of the relay are included between thetest-line con necting the plug-socket frames and earth; and Fig. 2 is alike diagram illustrative of the modification in which the test-line isabsolutely and directly earthed, the relay-helices being in a branchfrom the direct main conductor to earth.

In Fig. 1, O is a central station, to which any number of metalliccircuits W, extending from sub-stations S S 850., converge, and M is amultiple telephone-switchboard divided as usual into sections, to whichall lines loop and at which the said lines are represented byspring-jack plug-sockets J. Theline L of each circuit passes through itsseries of jackcontacts and also through the helices of itscall-annunciator A, these being apportioned in a manner well understoodbetween the several sections, so that at each section all circuits areaccessible for connections and a given number have their calls answered.The direct line of each metallic sub-station circuit I have, as alreadyintimated, designated by the letter L, the return-line by L and theextension of the latter through the switchboard by L R is a relay, whichin practice has been wound to about five hundred ohms and which isconstructed to have a high self-induction coefficient, so that itsimpedence to currents which have a high frequency of changesuch astelephone-currents-is very considerable.

X Y Z indicate the several operators sections of the multipleswitchboard M, and at each are a number of plug-and-cord connectors eachhaving a listening-key f in its circuit, whereby the operatorstelephones can be connected or disconnected at will in a bridge-circuitbetween the two conductors of the connecting-cord.

In the drawings for the avoidance of complication the telephones arecarried out at section X only. For each connecting-link at each sectionthere is a disconnecting or clearing-out annunciator A which also isbridged between the two conductors of its cord.

B is a test-battery or other suitable electric generator, which may becommon to the entire switchboard and which has one pole connected withthe earth at E. Its other pole.

connects with an omnibus-wire D, from which at suitable points 5, 6, and7 branches extend through retardation-coils O to connections at Swiththe flexible-cord conductor 30, which terminates in thatconducting-surface of the plug-connector that connects with the metallicjack-frame. Each spring-jack or plug-socket J consists ofa conductingframe or socket g, which receives the plug, a contact-spring s, and aresting contact-pin or anvil e therefor, on which the spring 8 normallyrests, but from which it is separated by the insertion of a'plug withinits socket, as is shown at section Z. Each connecting-plug P has anon-conducting handle 71, a sleeve or shank conducting-surface p adaptedto make contact with the spring-jack frames g, a tip-conducting piece1), adapted to make contact with the jacksprings, andseparating-insulation q. The tip-contacts of the two plugs of a pair areunited by cord conductor 29, and the sleevecontacts are united by cordconductor 30.

The telephone outfitin practice consists, as shown, of areceiving-telephoneTand atransmitter t, the latter being in circuit, asusual, with a local battery I) and the primary helix of aninduction-coil I, the secondary helix of the said induction-coil beingarranged for the sake of perfectly balancing the circuit in two parts i,one on each side of the receiver. The receiving-telephone T has aconnection 31 run from the central point of its helix to earth at E. Thetwo wires 25 and 26, extending as a loop from the telephones, connectwith the two inner springsz of the listening-keyf and are thusdiscontinuous in the recumbent potion of the key and connect with theircompanion springw in the elevated position thereof, the said springs'xbeing in turn united by wires 27 and 28, respectively, to the cordconductors 29 and 30 at the points 13 and 12, thus providing thebefore-mentioned bridgecircuit for the telephone.

A condenser c is interposed in the circuit of the tip-uniting cordconductor 29 for the purpose of preventing misleading sounds in thetelephone, while permitting the free passage of the voice-currents. Ifthis were not added, a current from the test-battery would I circulatethrough the testing-circuit part of the telephone-helix as soon as thelisteningkeyf is placed in the position to connect the telephones, andin that event the operation of making the. busy-test would cause aredistribution of such current and produce a signal in the telephonewhether the tested line were busy or not. I have hereinbefore indicatedthe course through the switchboard of the direct-circuit conductor L.The returnconductor L entering from the sub-station, terminates at thearmature lever a", with which it is electrically connected. This isnormally retracted by a counter -spring 3' against its back contact 0,from which a Wire 36 leads by way of the junctionl to an earthconnection 37, and the return-conductor is thereby normally connecteddirectly to earth. The electro-magnet of the relay or electromagneticinstrument R is connected in the circuit of acontinuationL of the saidreturnconductor, which starts from the earth connection at 37 and, afterpassing through the said magnet, ektends through the switch-f board,having its other end discontinuous and 5 having at eachswitchboard-section a branch d, extending to the proper socket-frame ortest-ring, these, also, being normally discontinuous. It will now beevident from whathas been statedthatthenormalor restingcon'dition" ofeach circuit is that the direct line L, coming in from the sub-station,passes through the separable contacts of a series of spring-jacks andthrough an annunciator atone section to earth; that the return-line Lcoming in, is grounded directthrough the relay-armature le-" ver andback contact, and that its continua= tion extends from earth through therelay-' coils and switchboard, being discontinuous and having branches,one to each of its own spring-jack frames. The insertion of aplugconnectorPat any section (shown at Z) closes the current of thetest-battery B through the relay-coils and the armature r is attracted.breaking the direct-earth connection of L and uniting L through thearmature-lever r,

' its front contact-stop c and the wire 38 electrically with itsextension L thus completing a metallic talking-circuit, to which,however, is attached an earth branch through the relay B. This, being ofhigh resistance and high electro-rnagnetic retardation, may be neglectedin practice' In the drawings it is assumed that'some circuit having itscall-annunciator at section X has called for circuit Wand that theoperator is applying the test plug P to ascertain whether W is busy orat liberty. Circuit W is, as we know, in connectiom with circuit W atsection Z and its relay armature is attracted forward, as shown. Beingso connect- 'ed, its jack-springs is by the plug-stem raised from itscontact 6, and the annunciatorAand terminal earth are disconnected. Thesleevecontact surface 19 of the plug being'in connection through itsconductor 30, its retardation-coil O, the' junction 5, and the bus-wireD with test-battery B, it is obvious that the circuit of said battery isclosed through the relay R by way of socket-frame g, branch line d,junction 4, conductor L relay R, and to earth, and that the relay holdsits armature forward. This battery connection also raises the potentialof the several jack-frames of the same circuit, they being all inconnection with the line L by their branches d, and when at-any sectionthe test-plug is applied, as

er-helix to earth.

shown at section X, a portion of the current of the test-battery isdiverted from the test frame g under test, through the operatorsreceiving-telephone by way of plug-tip p, cord conductor 29,junction-point 13, wire 27, keysprings a: and z, (the cam-key beingfirst turned up,) wire 25,induction-coil conductor '5, wire 38, andthrough one-half of the receiv- The current suddenly passing the momentthis circuit is closed by the application of the plug-tip to thesocket-frame, a sharp click is-heard in the telephone and denotes thatthe line is busy.

spring-jack frame or test-ring.

' The several retardation-coils C in the different cord circuits of thetest-battery prevent short-circuiting and also permit the use of agrounded test-battery without thereby introducing disturbance from theearth connection. The more important part of the busy-test concernsitself, however, with the testing of circuits where silence resultingfrom a test is required to have significance, since it is apparent thatan additional sound in the telephone to the required signal-sound isimmaterial, while the'occurrence of a sound when'no sound should beheardis at once a deceptive signal and does not'truly indicate 5 thecondition of the circuit. To illstrate this, let it be supposed that theplug P is not inserted into the socket at Z, that circuit W is thereforeat liberty, and that the armaturelever r of its relay is therefore atrest against its back contact 0. This condition being assumed, no truebusy-signal could be heard in the telephone for the reason that there being no plug-connector in any ofthe sockets of the circuit thetest-battery B has no connectionwith any of the test-frames, and hencethe application of the test-plug to any of the said frames does not andcannot determine the passage of a current through the testingtelephoneT, and the legitimate busy-signal is therefore not heard Were it not forthe r severance of the continuation-line L from the main return L or ofthe interposed earth connection, a click which would be mistaken for thetrue busy-signal "would in case of a charge on the metallic circuit beheard; but these conditions being present, it is obvious that no falsebusy-signal due to the above cause can be received, since in the firstplace the application of the test-plug simply provides thetesting-telephone with an earth connection through the relay by way ofsocket-frame g, branch wire d, junction 2, conductor L andrelay R, andnot with a charged .line, while in the second place the main return-lineL being connected'with the earth direct by the armature-lever 7',contact 0, and

wire 36, is constantly drained of its charge.

In Fig. 2 I show a modification in which the test-battery B is connectedthrough the usual retardation-coil O with the tip-uniting conductor 29of the pairs of plugs. In this case, while the main-line circuits andcircuit connecting and supervising apparatus is arranged generally inthe same way as in Fig. l, the connections of the relay R are different.Two line-circuits are here shown, W being a metallic and W anearth-completed circuit. The metallic circuit, entering from thesub-station by wire L, passes through the several spring-jack contactsfrom the spring 8 to the anvil-contacts e, and then through theannunciator A and by wire L to the returnconductor L which leads back tothe sub-station, branching, however, by wires d to eachTheearthcompleted sub-station circuit W is arranged much in the sameway, except that the sin gleline conductor L is grounded at thesub-station S and that the return-conductorthrough the switchboard L isalso connected to earth at a point external to the switchboard, abalancing-resistance V being included in its circuit. The electro-magnetof the relay R in this case is in a branch 42, leading to earth from apoint 41 on the main or direct-circuit conductor L, and as when thecircuit is idle no current traverses its coils its armature a" v isnormally retracted by its counter-spring and the lever thereof, which isconnected directly to earth, is held against its back-stop c, from whicha wire 43 is led to any point 40 on the test or return wire L By thisarrangement all the test-frames of the line under consideration are inconnection normally with earth direct and the main or spring contactside of the circuit is in connection with the earth through therelay-coils. I preferably provide an arrangement of apparatus inconnection with this mode of busy test which gives aspecialized signal.An electro-magnet F is included in a branch circuit w, which extends toan earth terminal from any point 44 on the telephone-conductor 25. Whenthe Us tening-key cam f is turned to the position shown at section X andits spring-contacts m and z thereby brought together, the magnet F isenergized by a current from test-battery B, which finds a closed circuitthrough it, attracting the armature f 'toa forward position. The leverof said armature hasa resilient reed extension f suitably weighted, sothat when it is retracted by its counter-spring it not only comes to asolid and permanent rest upon its back-stop f but also makes on itsbackward movement a snap or brief contact with the auxiliary back-stop fthereby closing for a moment a short circuit u, which includes thesecondary helix 2' of one induction-coil I and I telephone T when thesnap-contact between the reed f and its contact-stop f occurs.

' The vibrator k may be common to the entire central station, andconnections to other switchboard-sections are indicated by the wires 11.The resistance of secondary helix '5 of the induction-coil1 must besufficiently high that the telephone T will not be shortcircuitedthrough it.

In testing if We suppose the line tested to be at liberty-as, forexample, is W -the armature-lever of its relay R will rest against stopa, as shown. The operator, having turned up the cam f to bring thetelephone T lnto circuit and to energize magnet F, bringing the armature1" forward, touches the socketframe J 2 with the tip-contact of thetestingplug P. The line being at liberty, as stated, the testing-batteryB is momentarily shortcircuited by way of conductor D, point 7,retardation-coil 0, point 8, tip-conductor 29, plug-tip p, test-frame gof jack J wire (1, point 2, wire L point 40, wire 43, stop 0, armaturea", and wire 37. The result of the establishment of such a short circuitis that the current is drained from the magnet F and its armature-reedfalls back, making asnap-contact on the stop f causing an intermittentcurrent to circulate for a moment through the short circuit u andproducing a momentary buzz in the telephone T, which is inductivelyconnected therewith. This buzz indicates the circuit wanted to be atliberty, and is an unmistakably-true test, for it is im possible thatany discharge from the line can take place through the telephones inview of the earth connection 37 at the relay. If the line wanted bebusyas is line W, for instance, which has a plug inserted at section Znoshort circuit can be established upon touching the test/frame with theplug-tip, for the reason that the act of inserting the plug at section Zhas already closed the circuit through the direct line L andrelay-coilsR of main circuit W, and has consequently by the attractionof the relay-armature, as shown, separated the points 0 and 46. Hence inthis case the magnet F of the test apparatus continues to hold itsarmature forward and the vibrator cannot produce a signal in thetelephone. Silence in the telephone, therefore, in this instance,denotes that the line is already busy.

I claim 1. In a busy-test system and apparatus for multipleswitchboards, the combination of the main circuit having plug-sockets atthe several switchboard-sections, plug-and-cord con-v nectors foruniting the sockets of any two lines, a test-battery, a normally-opencircuit therefor capable of being closed by the insertion of saidplug-connectors in the socket of any main circuit, a relay orelectro-lnagnetic device connected with the main line and included inthe circuit of a conductor common to said main circuit and saidnormally-open local circuit, a direct-earth branch normally connectedwith one side of the main circuit through the armature of said relay andadapted to be disconnected when the said relay is energized by theinsertion of a plugconnector in any plug-socket of the main circuit, anda busy-test circuit in which the telephone is directlyor inductivelyincluded as an indicating-instrument and which is localized andprevented from giving false testsignals by the normal connection of thesaid relay-controlled earth branch, substantially as described.

2. In a multiple switchboard, the combination, with each main-linecircuit, of an earth branch normally connected therewith at a pointexternal to the said switchboard, an electrical generator, anormally-open local circuit therefor leading through the plugs-'-sockets of said line and adapted to be closed by the insertion of aplug-connector in any of said sockets, and a relay included in suchcircuit and'controlling the continuity of said earth branch,substantially as'described.

' 3. The combination, with a multiple switch board, main-line circuitsconnected therewith, each having a direct conductor extending through aseries of spring-jack contacts, and a return or test conductor branchingto the insulated conducting test frames or rings of thesaid-spring-jacks, a branch extending from a point on saidtest-conductor external to the spring-jacks to earth direct, and a relaycontrolling the said earth branch by means of its armature and itselfincluded in an earth branch from the direct main-line conductor, of aplug and connecting-cord therefor at any switchboard-section, wherebyany two spring-jacks may be connected, a test-battery connected with theconductor leading from the tip of such plug, and'a normally-open circuittherefor adapted to be closed through the relay for the purpose ofopening the earth branch upon the'insertion of a plug in its jack, atelephone associated with a pair of cord-connected plugs at a secondswitchboard section, connected induce tively with a vibratorycircuit-breaker, an electro-nlagn'et in a derived circuit of thetest-battery controlling the continuity of said inductive connection,maintaining the same open when its armature is attracted and momentarilyclosing the sanne, and thereby producing a signal in the telephone whenits armature is retracted, and connections whereby on the application ofthe test-plug to the testframe of any spring-jack thesaidelectromagnet'may be short-circuited'through the direct-earthbran'ch ofthe line tested, when the said line is at liberty and the signal therebygiven in the telephone, substantially as described.

In testimony whereof I have signed my name to this specification, in thepresence of two subscribing witnesses, this 3ls'tday of March, 1892.

' JAMES 'L. MQQUARRIE.

Witnesses: v

GEQWILLIS PIERCE, 7 V. M. BERTHOLD,

